Fabrication method for laminated films comprising Al-Si-Co alloy film and refractory metal silioide copper film

ABSTRACT

As a wiring for semiconductor devices, the wiring consisting of an Al-Si-Cu alloy film is excellent in the electromigration resistance but is inferior in the stressmigration resistance. In order to compensate this aspect a laminated film consisting of an Al-Si-Cu alloy film and a refractory metal silicide film began to be used as the wiring, but a wiring thus obtained has a weakness in that its electromigration resistance deteriorates. However, it is possible to suppress the deterioration in the electromigration resistance while maintaining the stressmigration resistance by adding Cu to the refractory metal silicide film. In particular, when the refractory metal silicide film is a tungsten silicide film, the concentration of Cu is preferable that it is in the range of 0.1 to 1.0 wt. %.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to semiconductor devices and fabricationmethods thereof, and more particularly to wirings for semiconductordevices composed of multi-layer type (laminated films) of an Al-Si-Cualloy film and a refractory metal (having high melting point) silicidefilm and fabrication methods thereof.

2. Description of the Prior Art

Aluminum-based alloy films have been used widely for a long time aswiring materials of semiconductor devices. In the old days, aluminumfilms alone had been used. As the depth of diffused layers became small,Al-Si alloy films began to be employed in order to deal with theso-called alloy spike phenomenon. With the patterns of the semiconductordevices becoming finer, the current density for wirings increased first,and the electromigration became an important problem in reliability.This phenomenon is accompanied with Si precipitation, micro-void growthand the like which could not be handled by means of the Al-Si alloyfilms. This is the reason why Al-Si-Cu alloy films became to beintroduced. Use of these alloy films cause CuAl₂ to be precipitated atthe grain boundaries, and CuAl₂ thus formed blocks the mass transport ofAl by the current. In addition, as the wiring width approaches the grainsize due to the patterns of the semiconductor devices becoming finer,the stressmigration phenomenon was made visible. Under thecircumstances, that the Al-Si-Cu alloy films are powerless against thestressmigration failure, laminated films consisting of an Al-Si-Cu alloyfilm and an refractory metal silicide film began to be introduced.

This laminated film is undoubtedly effective for stressmigrationfailure. However, this laminated film is inferior to the Al-Si-Cu alloyin electromigration resistance.

This fact was reported by an article titled "COMPARISON OFELECTROMIGRATION PHENOMENON BETWEEN ALUMINUM INTERCONNECTION OF VARIOUSMULTILAYERED MATERIALS" by T. Fujii et al. in the digest of papers forthe 1989 VMIC Conference sponsored by IEEE, pp. 477-483. This reportgives an analysis which focuses attention on the behavior of Si.

BRIEF SUMMARY OF THE INVENTION Object of the Invention

It is an object of the present invention to provide wiring forsemiconductor devices.

It is another object of the present invention to provide a highlyreliable wiring for semiconductor devices.

It is a further object of the present invention to provide wiring forsemiconductor devices which is excellent in electromigration resistanceas well as in stressmigration resistance.

It is a further object of the present invention to provide wiring forsemiconductor devices consisting of a laminated film of an Al-Si-Cualloy film and a refractory metal silicide film.

It is a further object of the present invention to provide a highlyreliable wiring for semiconductor devices consisting of a laminated filmof an Al-Si-Cu alloy film and a refractory metal silicide film.

It is a further object of the present invention to provide wiring forsemiconductor devices consisting of an Al-Si-Cu alloy film and arefractory metal silicide film which is excellent in theelectromigration resistance as well as in the stressmigrationresistance.

It is a further object of the present invention to provide amanufacturing method of a wiring for semiconductor devices.

It is a further object of the present invention to provide amanufacturing method of a highly reliable wiring for semiconductordevices.

It is a further object of the present invention to provide amanufacturing method of a wiring for semiconductor devices withexcellent electromigration resistance as well as stressmigrationresistance.

It is a further object of the present invention to provide amanufacturing method of a wiring for semiconductor devices consisting ofa laminated film of an Al-Si-Cu alloy film and a refractory metalsilicide film.

It is a further object of the present invention to provide amanufacturing method of a highly reliable wiring for semiconductordevices consisting of a laminated film of an Al-Si-Cu film and arefractory metal silicide film.

It is a further object of the present invention to provide amanufacturing method of a wiring for semiconductor devices consisting ofa laminated film of an Al-Si-Cu alloy film and a refractory metalsilicide film with excellent electromigration resistance as well asstress-migration resistance.

SUMMARY OF THE INVENTION

In a semiconductor device having a wiring consisting of an Al-Si-Cualloy film and a refractory metal silicide film, the semiconductordevice of the present invention has Cu added in the refractory metalsilicide film. It is preferable that the refractory metal silicide filmis a tungsten silicide film, a molybdenum silicide film. a tantalumsilicide film or a titanium silicide film. When the refractory metalsilicide film is a tungsten silicide film, the Cu concentration ispreferable to be in the range of 0.1 to 1.0 wt. %. A wiring consistingof a laminated film of an Al-Si-Cu alloy film and a refractory metalsilicide film with excellent stress-migration resistance can be obtainedby adding Cu to the refractory metal silicide film without deterioratingits electromigration resistance. The reasons for the limitations on theCu concentration when the refractory metal silicide film is a tungstensilicide film are as follows. When the Cu concentration is below 0.1 wt.%, the time median to failure (MTF) of electromigration is approximatelyequal to that of the case where Cu is not added to the tungsten silicidefilm. As the Cu concentration becomes higher than 0.1 wt. % the value ofMTF increases rapidly. On the other hand, when the Cu concentration ishigher than 1.0 wt. %, if an etching is given for forming wires of alaminated film consisting of an Al-Si-Cu alloy film and a tungstensilicide film with added Cu, and the wires are left standing, acorrosion is generated between Cu and Al caused by a local batteryeffect. However, for the Cu concentration below 1.0 wt. % there will notbe generated a corrosion even if the sample is left alone for a longtime.

In a method of manufacturing a semiconductor device having wires formedof a laminated film of an Al-Si-Cu alloy film and a refractory metalsilicide film, a first aspect of the present invention includes thefollowing steps. On one surface of a semiconductor substrate with aprescribed semiconductor elements formed thereon, there is deposited aninsulating film and a prescribed contact hole is opened in thusinsulating film to reach the semiconductor element. Then, a laminatedfilm consisting of an Al-Si-Cu alloy film and a refractory metalsilicide-Cu alloy film is formed all over the surface. Following that,the laminated film is etched by using a photoresist film as a mask.After removing the photoresist film, there is formed, by annealing, alaminated wiring consisting of the Al-Si-Cu alloy film and therefractory metal silicide-Cu alloy film. The refractory metalsilicide-Cu alloy film is preferable that it is a tungsten silicide-Cualloy film, a molybdenum silicide-Cu alloy film, a tantalum silicide-Cualloy film or a titanium silicide-Cu alloy film. When the refractorymetal silicide-Cu alloy film is a tungsten silicide-Cu alloy film,preferable Cu concentration of this film is in the range of 0.1 to 1.0wt. %. The reasons for the limitation on the Cu concentration when therefractory metal silicide-Cu alloy film is a tungsten silicide-Cu alloyfilm are the same as aforementioned.

In a method of manufacturing a semiconductor device with a wiringconsisting of a laminated film of an Al-Si-Cu alloy film and arefractory metal silicide film, a second aspect of the present inventionincludes the following steps. On one surface of a semiconductorsubstrate with a prescribed semiconductor element formed thereon, thereis formed an insulating film, and a prescribed contact hole is opened inthe insulating film to reach the semiconductor element. A laminated filmconsisting of an Al-Si-Cu alloy film and a refractory metal silicide-CuAlloy film is formed all over the surface. The Cu concentration of theAl-Si-Cu alloy film is smaller than the Cu concentration of therefractory metal silicide-Cu alloy film. Then, the laminated film isetched by using a photoresist film as a mask. After removing thephotoresist film, there is formed, by annealing, a laminated wiringconsisting of a laminated film formed by the Al-Si-Cu alloy film and therefractory metal silicide-Cu alloy film. It is preferable that therefractory metal silicide-Cu alloy film is a tungsten silicide-Cu alloyfilm, a molybdenum silicide-Cu alloy film, a tantalum silicide-Cu alloyfilm or a titanium silicide-Cu alloy film. When the refractory metalsilicide-Cu alloy film is a tungsten silicide-Cu alloy film, preferableCu concentration of this film is in the range of 0.1 to 1.0 wt. %. Thereasons for the limitation on the Cu concentration when the refractorymetal silicide-Cu alloy film is a tungsten silicide-Cu alloy film is thesame as aforementioned.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other objects, features and advantages of thisinvention will become more apparent by reference to the followingdetailed description of the invention taken in conjunction with theaccompanying drawings, wherein:

FIGS. 1A and 1B are diagrams for elucidating the cause of deteriorationin the electromigration resistance in the conventional laminated wiringconsisting of a laminated film of an Al-Si-Cu alloy film and arefractory metal silicide film, in which FIG. 1A is a graph showing thedepth profile obtained by SIMS of a laminated film of an Al-Si-Cu filmand a refractory metal silicide film as deposited, and FIG. 1B is agraph showing the depth profile obtained by SIMS of a laminated film ofan Al-Si-Cu film and a refractory metal silicide film after annealing;

FIGS. 2A to 2C are schematic sectional views for describing the methodof manufacturing a first embodiment of the present invention, arrangedin the order of manufacturing steps;

FIG. 3A is a graph showing the depth profile obtained by SIMS of alaminated film as deposited of an Al-Si-Cu alloy film and a tungstensilicide-Cu alloy film in a first embodiment of the present invention.Further, FIG. 3B is a graph showing the depth profile obtained by SIMSof the laminated film after annealing of the Al-Si-Cu alloy film and thetungsten silicide-Cu alloy film;

FIG. 4A is a graph showing the MTF value in normalized form for theelectromigration resistance of the laminated film of the Al-Si-Cu alloyfilm and the tungsten silicide-Cu alloy film of the first embodiment ofthe present invention;

FIG. 4B is a schematic sectional view of the sample for the measurementin FIG. 4A;

FIG. 5 is a graph showing the corrosion resistance time of a sampleobtained by etching the laminated film of the Al-Si-Cu alloy film andthe tungsten silicide alloy film of the first embodiment of the presentinvention, as a function of the Cu concentration in the tungstensilicide-Cu alloy film and;

FIGS. 6A to 6D are sectional views for describing the method ofmanufacturing a second embodiment of the present invention as arrangedin the order of manufacturing steps:

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before proceeding to the description of the embodiments of the presentinvention, the history which led to the present invention is in order.

As described in the above, the electromigration resistance of alaminated film formed by an Al-Si-Cu alloy film and a refractory metalsilicide film is inferior to that of a single layer film consistingexclusively of an Al-Si-Cu alloy film. The present inventor pursued thecause of the above-mentioned phenomenon from a view-point which isdifferent from that reported by T. Fujii et al. in the digest of papersfor the 1989 VMIC Conference, pp. 477-483.

Namely, after forming a silicon oxide film on a silicon substrate, aWSi_(x) (x=2.5-3.0) film with thickness of 0.2 μm is deposited, andfurther an Al-1% Si-0.5% Cu film with thickness of 1.0 μm is depositedon top of it (% signifies wt. % hereinafter). The depth profile of thefilms as deposited determined by the SIMS measurement is shown in FIG.1A. Then, the sample is annealed for 30 minutes at 450° C. in anatmosphere of the mixed gas of H₂ and N₂. The depth profile of thesample after annealing determined by the SIMS measurement is as shown inFIG. 1B. An oxygen beam is used for etching the sample in thismeasurement. The ordinate shows the ratio of the counts per second ofeach ion to the counts per second of oxygen used as the reference. Whatis of importance here are the relative changes in each of the ions andthe reference. Suppose that one pays attention to Cu. In the asdeposited state, Cu exists exclusively in the Al-Si-Cu film. However,following an annealing Cu is distributed substantially uniformly in theAl-Si-Cu film and the WSi_(x) film. This is accomplished by thediffusion of Cu from the Al-Si-Cu film to the WSi_(x) film. Of thediffusing Cu ions it is considered that those from CuAl₂ in the grainboundaries dominate over those from the grains in the Al-Si-Cu film.Because of this, it is considered that the CuAl₂ concentration in thegrain boundaries is lowered as a result of annealing, and the masstransport blocking power of Al in electromigration is reduced.

Based on the findings in the above, the present inventor proposed thefollowing as the methods of suppressing the reduction in theelectromigration resistance of the laminated film of the Al-Si-Cu filmand the refractory metal silicide film. A first method is to keep the Cuconcentration in the Al-Si-Cu alloy film high in advance. A secondmethod is to add Cu to the refractory metal silicide film in advance.Further, a third method is to set the concentration of Cu to be added inadvance to the refractory metal silicide film to be higher than the Cuconcentration in the Al-Si-Cu film so as to generate a Cu diffusion fromthe side of the refractory metal silicide film to the side of theAl-Si-Cu alloy film. It is thought that an extreme example of this caseis the method of converting by annealing the Al-Si alloy film of alaminated film of an Al-Si alloy film and a refractory metal silicidefilm with added Cu to an Al-Si-Cu alloy film.

The first method brings about an inconvenience in the etching of theAl-Si-Cu alloy film so that it was not tried.

Next, referring to the drawings, the present invention will bedescribed.

FIGS. 2A to 2C are schematic sectional views as arranged in the order ofmanufacturing steps for describing the first embodiment of the presentinvention.

First, as shown in FIG. 2A, a silicon oxide film 11 is formed on thesurface of a silicon substrate 10 with a semiconductor element formedthereon (not shown), and a contact hole that reaches a required part ofthe semiconductor element is opened in the silicon oxide film 11. Next,a WSi_(x) -Cu alloy film 12 (x=2.5-3.0) obtained by adding 0.1-1.0 wt. %of Cu to a WSi_(x) is deposited by sputtering on the entire surface to athickness of 20-200 nm.

Then, as shown in FIG. 2B, an Al-Si-Cu alloy film 13 with thickness of0.3-2.0 μm is deposited on top of it by sputtering. The Si concentrationin the Al-Si-Cu alloy film 13 is 1.0 wt. %, and the Cu concentration isin the range of 0.3-1.0 wt. %.

Next, as shown in FIG. 2C, the Al-Si-Cu alloy film 13 and the WSi_(x)-Cu alloy film 12 are etched sequentially using a photoresist film (notshown) having the same shape as the wiring in a mask, thereby forming alaminated film having the same shape as the wiring. The etching methodadopted is that of RIE that uses a mixed gas of Cl₂ and BCl₃ (CF₄ may beadded). Subsequently, after removing the photoresist film the sample isannealed for 30 minutes in an atmosphere of mixed gas of H₂ and N₂. As aresult, there is formed a laminated wiring consisting of the Al-Si-Cualloy film 13a and the WSi_(x) -Cu alloy film 12a.

FIGS. 3A and 3B show the depth profiles of the laminated wiring of thepresent embodiment. The thickness of the Al-Si-Cu alloy film is 1 μm,and the concentrations of Si and Cu in the Al-Si-Cu alloy film are 1.0wt. % and 0.5 wt. %, respectively. In addition, the thickness of theWSi_(x) -Cu alloy film is 0.2 μm, and the Cu concentration in theWSi_(x) -Cu alloy film is 0.5 wt. %. As shown in FIG. 3A, the Cuconcentration in the state of as deposited is approximately uniformwithin the laminated film although there exist certain variations.Further, as shown in FIG. 3B, the Cu concentration is substantiallyuniform within the laminated film in the state of after annealing.

Referring to FIGS. 4A and 4B, a description will be given concerning theelectromigration resistance of the laminated wiring formed in thepresent embodiment. FIG. 4B is a schematic view of the sample used forthe measurement of the electromigration resistance. The sample for themeasurement is constructed as follows. A silicon oxide film withthickness of 0.3 μm is formed on a silicon substrate, and a WSi_(x) -Cualloy film with thickness of 0.1 μm is formed thereon. The Cuconcentration in the WSi_(x) -Cu alloy film is y wt. % (y=0-5).Following that, an Al-Si-Cu alloy film with thickness of 1.0 μm isformed on top of it. The Si and Cu concentrations within the Al-Si-Cualloy film are 1.0 wt. % and 0.5 wt. %, respectively. A laminated wiringis formed by etching and annealing the laminated film. Further, asilicon nitride film with thickness of 0.5 μm is formed on top of it byplasma CVD method. FIG. 4A shows the measurement result of MTF whereinone half of the wires are disconnected due to electromigration under theconditions of a temperature of 200° C. and a current density of 2×10⁶A/cm². In the figure, the ordinate is the value of the MTF of thelaminated wiring consisting of a WSi_(x) -Cu alloy film and a Al-Si-Cualloy film normalized with respect to the MTF of a laminated wiringconsisting of a WSi_(x) film and an Al-Si-Cu alloy film. The abscissashows the Cu concentration in the WSi_(x) -Cu alloy film. From thefigure the following can be observed. That is, although the MTF ishardly improved for the Cu concentration of 0.06 wt. % in the WSi_(x)-Cu alloy film, the electromigration resistance is improved when the Cuconcentration becomes over 1.0 wt. %.

FIG. 5 is a graph showing the corrosion resistance time of the laminatedwiring versus the Cu concentration in the WSi_(x) -Cu alloy film of thepresent embodiment. Here, the corrosion resistance time is defined asthe duration (number of days) between the time at which the laminatedfilm formed on the silicon substrate is left standing in the atmosphereafter it is etched with the photoresist as a mask and the time when acorrosion is first observed. The corrosion is conjectured to be formeddue to a local battery effect between Al in the Al-Si-Cu alloy film andCu in the WSi_(x) -Cu alloy film. From the figure it can be observed forthe Cu concentration in the WSi_(x) -Cu alloy film higher than 1.0 wt. %that the corrosion resistance time is reduced with the increase in theCu concentration. For example, the corrosion resistance time is 24 daysfor the Cu concentration of 1.2 wt. %. In contrast, when the Cuconcentration in the WSi_(x) -Cu alloy film is below 1.0 wt. %, nocorrosion is observed even if the laminated film is left alone for about200 days. A corrosion resistance time of about 24 days will be of nospecial problem from the production viewpoint, but it will become of aserious concern from the reliability view point. In this case themoisture resistance of the semiconductor device will be reduced.Accordingly, preferable Cu concentration in the WSi_(x) -Cu alloy filmis below 1.0 wt. %.

As has been described in the above, in the present embodiment thedeterioration in the electromigration resistance can be suppressed whileholding the stress-migration resistance if the Cu concentration in theWSi_(x) -Cu alloy film is set to the range of 0.1 to 1.0 wt. %.

In the present embodiment, the description has been presented in termsof a laminated wiring consisting of an upper layer of an Al-Si-Cu alloyfilm and a lower layer of a WSi_(x) -Cu alloy film. However, an effectsimilar to that of the present embodiment can be obtained for alaminated film, for example, consisting of an upper layer, anintermediate layer and a lower layer of a WSi_(x) -Cu alloy film, anAl-Si-Cu alloy film and a WSi_(x) -Cu alloy film, respectively.Similarly, it will be obvious that an effect similar to that of thepresent embodiment can also be obtained for laminated films using othercombinations of the two kinds of the alloy films, such as a laminatedfilm with an Al-Si-Cu alloy film for the upper and the lower layers anda WSi_(x) -Cu alloy film for the intermediate layer.

It should also be mentioned that the present embodiment has beendescribed in conjunction with a WSi_(x) -Cu alloy film. However, apartfrom the numerical limitations on the actual values, it is also possibleto suppress the deterioration of the electromigration resistance, whilemaintaining the stressmigration resistance of wires consisting of alaminated film of an Al-Si-Cu alloy film and a refractory metal silicidefilm by adopting a molybdenum silicide film, tantalum silicide film or atitanium silicide film as the refractory metal silicide film and addingCu to such a film.

FIGS. 6A to 6D are schematic sectional views arranged in the order ofmanufacturing steps of a second embodiment of the present invention.This embodiment is an example extreme case wherein the concentration ofCu to be added in advance to a refractory metal silicide is made higherthan the Cu concentration in an Al-Si-Cu alloy film so as to generate adiffusion of Cu from the side of the refractory metal silicide to theside of the Al-Si-Cu alloy film. In other words, in the presentembodiment the Al-Si alloy film is converted to an Al-Si-Cu film byannealing the laminated film of the Al-Si alloy film and the refractorymetal silicide film to which is added Cu.

First, as shown in FIG. 6A, a silicon oxide film 21 is formed on thesurface of a silicon substrate 20 with a semiconductor element (notshown) formed thereon, and a contact hole reaching a required part ofthe semiconductor element is opened in the silicon oxide film 21. Next,a WSi_(x) -Cu alloy film 22 obtained by adding 0.9 wt. % of Cu to aWSi_(x) (x=2.5-3.0) is deposited by sputtering on the entire surface toa thickness of 0.2 μm.

Next, as shown in FIG. 6B, an Al-Si alloy film 24 with thickness of 1 μmis deposited on top of it by sputtering. The Cu concentration in theAl-Si alloy film 24 is 1.0 wt. %.

Then, as shown in FIG. 6C, the Al-Si alloy film 24 and the WSi_(x) -Cualloy film 22 are etched sequentially by using a photoresist film (notshown) having the same shape as the wiring in a mask, and a laminatedfilm consisting of an Al-Si alloy film 24a and a WSi_(x) -Cu alloy film22a with the same shape as the wiring is formed. The etching methodadopted is that of an RIE which uses a mixed gas of Cl₂ and BCl₃ (CF₄may also be added).

Then, as shown in FIG. 6D, after removing the photoresist film, anannealing is given for 30 minutes at 450° C. in the atmosphere of amixed gas of H₂ and N₂. As a result, the Al-Si alloy film 24a isconverted to an Al-Si-Cu alloy film 23a, and a laminated wiringconsisting of the Al-Si-Cu alloy film 23a and the WSi-Cu alloy film 22ais formed. The Cu concentration in the Al-Si-Cu alloy film formed byconverting the Al-Si alloy film is 0.12 to 0.15 wt. %.

In the present embodiment, analogous to the case of the firstembodiment, it is also possible to suppress the deterioration of theelectromigration resistance while maintaining the stressmigrationresistance.

Although the invention has been described with reference to specificembodiments, this description is not meant to be construed in a limitingsense. Various modifications of the disclosed embodiment, as well asother embodiments of the invention, will become apparent to personsskilled in the art upon reference to the description of the invention.It is therefore contemplated that the appended claims will cover anymodifications or embodiments as fall within the true scope of theinvention.

I claim:
 1. A method of manufacturing a laminated wiring for asemiconductor device in which the laminated wiring, formed on aninsulating layer on a semiconductor substrate and comprising analuminum-silicon-copper alloy film and a refractory metalsilicide-copper alloy film, is in contact with a portion of a majorsurface of said semiconductor substrate through at least one contacthole formed in said insulating layer, said method comprising the stepsof:forming the insulating film having at least one contact hole on amajor surface of said semiconductor substrate; forming a laminated filmincluding a first alloy layer including aluminum, silicon, and copperand a second alloy layer including silicon, copper, and a refractorymetal selected from the group consisting of tungsten, molybdenum,tantalum and titanium on said insulating layer and said portion of themajor surface; selectively etching said laminated film to form alaminated pattern; and thereafter annealing said laminated patternthereby converting said pattern to said laminated wiring.
 2. A method ofmanufacturing as claimed in claim 1, wherein said refractory metalsilicide-copper alloy film is a tungsten silicide-copper alloy film andthe concentration of the copper in said tungsten silicide-copper alloyfilm is in the range of 0.1 to 1.0 weight percent.
 3. A method ofmanufacturing as claimed in claim 1, wherein the concentration of copperin said refractory metal silicide-copper alloy film is higher than theconcentration of copper in said aluminum-silicon copper alloy film.
 4. Amethod of manufacturing as claimed in claim 3, wherein said refractorymetal silicide-copper alloy film is a tungsten silicide-copper alloyfilm and the concentration of copper in said tungsten silicide-copperalloy film is in the range of 0.1 to 1.0 weight percent.